This invention relates to a valve, and more particularly to an improved valve of the kind which has a spherical or part-spherical valve closure member operated through 90xc2x0 from the fully closed position to the full open position or vice versa.
Valves with spherical or part-spherical valve closure members are used extensively in the hydrochemical and beverage industries because of their relative ease of operation, their improved sealing characteristics, the fact that no mineral lubrications are needed to reduce operating torques and assist sealing and because problems related to line product contamination are reduced. In recent years the annular valve seat which works in conjunction with other valve control members has mainly been made from polytetrafluoroethylene (PTFE), this presenting a low friction operation on a firm surface to the valve control member. In many applications a valve seat of polymer materials may be suitable, but PTFE is preferred because of the ability to produce positive isolation with low operating torques and the general acceptance of the compatible nature of the PTFE when in contact with many hydrochemical and beverage applications.
The disadvantage of PTFE seated valves is that pressure and temperature can exceed the mechanical properties of the polymer seat construction which normally starts to occur around 230xc2x0 C. With increasing temperatures beyond 230xc2x0 C. the material will start to decompose. With extreme heat such as direct fire on the valve the PTFE seat will vaporise requiring the valve to have an emergency secondary metal backup seat incorporated in the internal seat housings. This is not an optimum solution because the closed valve control member will not engage on the secondary metal seat until the PTFE has fully vaporised, allowing the valve control member to re-seat onto the secondary emergency metal seat and constrain further line media from passing through the valve. If the heat around the valve is not sufficient fully to vaporise and decompose the PTFE seat a partial destruction of the PTFE seat will result and restrict the valve control member from sealing on the secondary emergency metal seat with the line media continuing to pass through the valve.
Other problems associated with PTFE seats are the vulnerability to damage or erosion from particles or solids suspended in the media passing through the valve. Valves with plug type valve control members suffer from high operating torques and rely on lubrication to reduce the torque and also assist the sealing. The disadvantage of this principle is that many types of media, such as liquid gasses and chemical solvent, dissolve the lubrication which has to be replaced at frequent intervals.
A principal object of the present invention is to improve upon known valves by providing a valve which will operate substantially without lubrication and will be substantially unaffected by the combination of high temperatures and pressures. Another object of the invention is to provide a valve of the kind having a spherical or part-spherical valve control member which will be relatively cheap and simple both to manufacture and to assemble and which will be relatively maintenance free in use and which will be versatile in its applications in the hydrochemical and beverage industries.
In accordance with one aspect of the present invention there is provided a valve having a spherical or part-spherical valve control member, the control member being rotatable within a valve housing to obturate or to open at least one opening of the housing by bringing a passage through the valve member out of or into alignment with said opening and a valve seat consisting of a radially outer disc portion which lies in a plane transverse to the axis of said opening and a radially inner generally frusto-conical, annular extension free at its narrower-diameter end and meeting the disc portion over a corner, the frusto-conical extension being adapted to lie in said opening with its larger-diameter end inward of the housing and to make substantially a line contact with the spherical or part-spherical surface of the valve member when the latter obturates said opening, the disc portion being supported by the housing in such manner that a radially inner region of the disc portion is capable of flexing.
Preferably said extension is resilient and the arrangement is such that the valve member tends to expand the extension in the assembled condition of the valve and/or when the valve member obturates said opening.
Preferably the extension of the valve seat is of metal, such as high nickel alloy steel.
Preferably the disc portion is supported by being gripped only at an outer periphery thereof, whereby an inner peripheral region of the disc is free to deform.
The valve may have a part-spherical valve control member and the axis of rotation of the valve control member is preferably offset from the center of the sphere on which the part-spherical surface of the valve control member lies toward the said opening such that as the valve member moves toward the opening-obturating position it tends to expand the extension of the valve seat.
Alternatively the valve may have a spherical valve control member through which a passage is formed, said passage aligning with openings on opposite sides of the valve housing when the control member is rotated to the valve-open position, each said opening containing a said valve seat and the dimensions of the valve housing may be such relative to the diameter of the sphere of the control member that when the valve is assembled the extensions of both of the valve seats tend to be expanded by the valve control member at least in the obturating position of the latter.
The or each said valve seat may be made by spinning into a frusto-cone an inner peripheral region of an annular disc of high nickel alloy steel.